This invention relates generally to electrical switches and, more particularly, to multiple push button switches having a short stroke and other improved features.
Multiple push button switches are well-known and are used in a wide variety of electrical equipment. Examples of such switches include those frequently used in household appliances, such as blenders, food processors, electric ranges, washing machines and air conditioners. A specific example of one such switch is shown in U.S. Pat. No. 4,362,912 to Woodward which is commonly assigned to the assignee of the present invention. Another switch of this general type (but which is disclosed in a single push button embodiment) is shown in U.S. Pat. No. 3,858,018 to Walley, which is also assigned to the assignee of the present invention. To the extent necessary for a full appreciation and understanding of the present invention, U.S. Pat. Nos. 3,858,018 and 4,362,912 are hereby incorporated by reference in their entireties into the present specification.
Switches such as those shown in the above-referenced patents are primarily mechanical devices in which one or more axially movable push rods interact with one or more laterally movable elongate sliders to open or close one or more electrical switch contacts. Such devices are reliable and relatively inexpensive, and are well-suited for applications such as those discussed above.
Alternative switch arrangements which may be suited for or adapted to these same applications include solid-state devices and membrane switches. The former may include touch-sensitive switches which may, for example, be activated by the capacitance associated with an operator who touches certain areas of a control panel or keypad. The latter may include switches in which two electrically conductive layers are separated by an insulator which is compressive to allow selected areas of the conductive layers to make contact with one another in response to pressure exerted by an operator. Both types of switches may be used in combination with additional devices (e.g., logic circuits) to effect the desired degree of control over a plurality of electrical circuits or elements. Both types of switches are relatively more complex than the mechanical switches described in the patents referenced above, and may be more expensive to manufacture, maintain or replace than the mechanical type switches discussed in those patents. However, both types of switches do have certain advantages over the mechanical type switches. For instance, both solid-state and membrane devices may be used in the design of a control panel which is essentially flat and which is not penetrated by one or more push rods required to actuate the switch. Such control panels are desirable for aesthetic reasons and for the ease with which they may be wiped or cleaned. Non-penetration of the control panel reduces the possibilities for contamination of interior components with dirt, moisture or other matter. Other features, such as lighted indicators, are relatively easily provided with switches of this type.
Among the several objects of the present invention is the provision of an improved electrical switch having advantageous or desirable features which are not present in the switches disclosed in the above-referenced patents. A more specific object of the invention is the provision of a push button switch which has a relatively short operating stroke, as compared to prior art switch assemblies, and which may be used with a flexible membrane such that a push rod of the switch may be axially displaced by a distance effective to open or close a pair of switching contacts by pressure exerted on a surface of the membrane. This structure allows the switch of the present invention to be used in combination with a flexible membrane and, thus, to offer advantages not previously associated with mechanical-type switches (i.e., switches which require that a push rod travel a relatively long axial distance and penetrate the surface of a control panel to effect a switching operation). Another object of the invention is to provide a push button switch having a relatively short stroke in which "teasing" of the contacts by unintended movements of the push rod or sliders is substantially reduced or restricted.
These and other objects of the present invention are achieved in an electrical switch assembly which comprises a housing, switch means mounted within the housing, a plurality of push rods extending through the housing and a plurality of generally elongate sliders movably mounted within the housing. The switch means preferably comprises a plurality of paired electrical contacts selectively movable to open and closed positions. The push rods have a first end, which is rolled or otherwise formed to have an enlarged cross-section, which terminates within the housing, and a second end which terminates exteriorly of the housing. The push rods are axially movable relative to the housing between at least a first (extended) position and a second (depressed) position. Each of the elongate sliders has a first edge and a first plurality of cam surfaces formed on the first edge for interacting with the paired electrical contacts of the switch means to selectively open and close the contacts as the slider moves within the housing. Each of the sliders further has a second edge and a second plurality of cam surfaces on the second edge for interacting with the first ends of respective ones of the push rods as the push rods are moved between the first and second positions. Each of the first ends of the push rods interacts with selected ones of the cam surfaces to cause respective ones of the sliders to move. Each of the cam surfaces on the second edges has a first portion having a first angle, relative to an axial centerline of a respective push rod, which is selected so as to require that a first predetermined level of force be applied to the push rod to cause the respective slider to begin to move away from the first position. Each of the cam surfaces also has a second portion having a second angle selected so as to require a second, substantially lower level of force be applied to the push rod to cause the respective slider to continue to move to the second position.
In one embodiment of the invention, the first portion of the second cam surface forms an angle of approximately 15.degree. with a plane which extends through the first portion of the cam surface and perpendicularly to the axis of the push rod. The second portion of the second cam surface forms an angle with this plane which is substantially greater than 15.degree.. In this embodiment, the first portion is a substantially flat surface. The second portion also comprises a substantially flat surface which extends from an edge of the first portion at an initial angle which is substantially greater than 15.degree.. The second portion of the cam surface can, alternatively, be curvilinear in shape.
Each of the first plurality of cam surfaces comprises a first portion, a second portion and a transition portion connecting the first and second portions. The first portion of each cam surface is aligned, in non-engaging relation, with a respective one of the electrical contacts as the slider moves away from the first position in response to the interaction between the push rod and the first portion of the second cam surface. The transition portion engages the electrical contact when the first end of the push rod is in the vicinity of an intersection of the first and second portions of the second cam surface. The transition portion interacts with the electrical contact to move the contact to an open or closed position as the slider continues to move to the second position in response to the interaction between the push rod and the second portion of the second cam surface. A "notch" or depression is provided in the second portion of the first camming surface to receive a portion of the movable switch contact to reduce unintended movements (e.g., vibrations) of the slider and/or electrical contact.
In one embodiment of the invention, the axial displacement of the push rod required to cause a slider to move from the first position to the second position is approximately 1/16 inch. The lateral distance traveled by the slider in moving from the first position to the second position is approximately 0.130 inch. This embodiment may further comprise a flexible membrane having first and second surfaces and being disposed such that the second ends of the push rods lie immediately adjacent the second surface of the membrane such that the push rods can be actuated by a force applied to an opposing portion of the first surface of the membrane. The membrane may be at least partially translucent or transparent. A light or other visible indicator may be disposed adjacent the second surface of the membrane.
In an alternative embodiment of the invention, a single push rod interacts with a pair of generally elongate sliders movably mounted within the housing. Each of the sliders has a cam surface on a first edge for interacting with the paired electrical contacts of the switch means, and a cam surface on a second edge for interacting with the first end of the push rod. As the push rod is axially moved, the sliders move in opposite directions within the housing. The cam surfaces on the second edges of the pair of sliders cooperatively interact with the electrical contact so as to cause the switch means to open and close in response to the concurrent and opposing movements of the sliders. In this embodiment, the axial movement of each push rod is short enough to allow the use of a flexible membrane adjacent the push rods to provide a flat, smooth surface on a control panel. Due to the cooperative interaction between the sliders, the lateral distance traveled by each slider in response to the axial displacement of the push rod is substantially decreased. In one embodiment of the invention, this distance is approximately 0.095 inch.
Each of the embodiments of the switch of the present invention include features which are intended to reduce or eliminate "teasing" of the electrical contacts by unintended movements of the sliders and push rods. In the embodiment of the invention just described (wherein two sliders cooperatively interact to open or close an electrical contact), the cam surfaces on the first edges of the sliders form a "V" which interacts with the electrical contact to prevent unintended movements of the sliders when the electrical contact is in at least one of the open and closed positions. In the embodiment of the invention in which a single slider interacts with the electrical contacts, this "anti-teasing" function is performed by the first portion of the second cam surface and the "notch" formed in the second portion of the first cam surface.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.